J72 with US2078 kit - Pump runs continuously.

Diagnose J72 Parking Brake - Pump Running Continuously.

Symptom(s)

Situation in which symptom(s) occurs:

• Ignition is on, and the parking brake button is pressed in, then the coach is placed in gear.

What happens then:

• Parking brake pump runs and builds pressure enough to release parking brake, but the pump continues to run. Or the pump runs but the brake is not releasing.
  

Cause

Gather information needed:

1. Chock wheels of coach.
2. Obtain a hydraulic pressure gauge that is capable of reading pressures above 2000 psi with a tee that allows you to install it in a #4 JIC connection.
3. Install pressure gauge at pump head. This will install where the hose is connected to the pump. You will remove the hose and install the tee with the pressure gauge between the hose and fitting in pump.
4. Once pressure gauge is installed, operate parking brake by turning the ignition on (with the engine not running); Press the yellow parking brake knob, then place the coach into the drive position.
5. Read the pressure indicated by the pressure gauge that was just installed.
6. This pressure should be above 1300 psi and below 1500 psi.

Testing to find the failure:

Pump does not reach 1300 psi

1. If the pressure does not reach a minimum of 1300 psi then the pump is recirculating, or has internally failed.
   1. If the pump is recirculating, then it would be caused by either failed veins, a failed internal bypass valve, the pressure solenoid, or the coil for it.
   2. The veins, and internal bypass valve are non serviceable. The pump would have to be replaced if that is the failure.
2. The pressure solenoid blocks the return path for the fluid, forcing it to build fluid pressure in the brake to release it.
   1. Fist check to ensure you are getting 12v and a good ground to the coil when the pump is running.
      1. If you are not getting 12v or ground to the solenoid then refer to the controller diagnostics article. 
   2. If the pressure solenoid is not seating then the pump would just run because it cannot build any/enough pressure to open the pressure switch.
      1. If the pressure solenoid is failed/failing then there really is no way to test it other than replacement. You can use part# W8001114-US
      2. You can try to remove it, and clean it, in the hope that there may have been some small debris that was blocking it from seating.
         1. If you chose to clean the valve then you would want to use brake clean and compressed air. Once you are ready to reinstall the valve after cleaning, lubricate the o-rings with Dexron ATF. Then install it using a torque value of 25 lb. ft.
3. The recirculating could be caused by a failed coil on the pump pressure solenoid.
   1. To test the coil, you can see if the coil is creating a magnetic field by placing a paper clip next to it while the pump is operating, and see if the paper clip sticks to it. If it does then the coil is functional.

Pump exceeds 1500 psi

1. The pressure switch is in charge of shutting off the pump motor when the pressure reaches the 1300-1400 psi that is required for the system.
   1. When the pressure reaches the 1300-1400 psi that is required, the pressure switch should open and disable the pump motor relay, in turn stopping the pump motor.
   2. If the pressure switch does not open, then the pump motor would continue to run to the point that it opens the internal bypass valve. This would then allow the excess fluid pressure to be recirculated back to the reservoir as the pump motor runs.
      1. To test the pressure switch, unplug it while the pump motor is running.
         1. If the pump motor stops running when the switch is unplugged then the pressure switch is failed.
         2. If the pump motor does not stop running when the switch is unplugged then the pump motor relay is failed.

Resolution

• If the pump has failed.
  • Use part# W8005231-US for replacement.
• If the solenoid or coil has failed.
  • Sold as a set. Use part# W8001114-US for replacement.
• If the pump motor relay is failed.
  • Please call with your VIN so we can look up the correct replacement for you coach.

You can find the product being discussed here: US2078